Thin film forming method

ABSTRACT

A method for forming thin films of a semiconductor device is provided. The thin film formation method presented here is based upon a time-divisional process gas supply in a chemical vapor deposition (CVD) method, where the process gases are supplied and purged sequentially, and additionally plasma is generated in synchronization with the cycle of pulsing reactant gases. A method of forming thin films that possess a property of gradient composition profile is also presented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/297,867, filed Jul. 15, 2003, now U.S. Pat. No. 7,141,278, issuedNov. 28, 2006, entitled “THIN FILM FORMING METHOD,” which is thenational phase application of PCT/KR01/00974, filed Jun. 8, 2001, andclaims priority from Korean Application No. 2000-31367 filed Jun. 8,2000; and Korean Application No. 2001-3830 filed Jan. 26, 2001, whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin film formation method, and moreparticularly, to a method for forming a metal film, a metal oxide filmor a metal nitride film that can be used as an insulating layer, adielectric layer, or an interconnect layer in a semiconductor orflat-panel display substrate.

2. Description of the Related Art

In the prior art, a metal film, a metal oxide film, or a metal nitridefilm have been formed by means of a physical vapor deposition (PVD)method such as sputtering. However, PVD is known to have poor stepcoverage and produce a non-even surface due to an overhang phenomenonwhere the opening of a hole or a trench is closed before the hole ortrench are fully filled. For these reasons, chemical vapor deposition(CVD) methods that form a layer having a relatively uniform thicknesswith good step coverage has been widely used in recent years.

However, for the conventional CVD technique, the source materialsrequired to form a layer are supplied at the same time, and therefore itis difficult to form a target layer having a desired composition andproperty. In addition, reaction of a variety of materials used to form alayer occurs in the gas phase, thereby causing the generation ofcontamination particles. When a multicomponent metal oxide such asbarium titanate (BaTiO₃) or barium strontium titanate ((Ba,Sr)TiO₃) isdeposited by CVD, the metals react with each other. As a result, itbecomes difficult to form a layer having a uniform composition over alarge area on the surface of a 300-mm wafer. In case of a CVD processwhere an organometallic compound is used as a source material, a largenumber of carbonic impurities are generated in the resulting film byraising the temperature of the substrate in order to increase the rateof film formation.

As a method of forming a thin film using a chemical compound material,an atomic layer deposition (ALD) method in which reactant gasescontaining the respective atoms of the compound are sequentiallysupplied is disclosed in U.S. Pat. Nos. 4,058,430 and 4,389,973 issuedto Suntola et al. in 1977. According to the ALD method, the thickness ofa layer formed on a substrate by the absorption of reactant gases isalmost constant regardless of the duration of reactant gas supply. Thus,the thickness and composition of a target layer can be accuratelyadjusted by varying the number of pulsing cycles of the source gases.However, ALD methods require separate pulses of reactant gasescontaining respective constituent elements. Therefore, when amulticomponent metal oxide film is formed by ALD, the thin filmformation process become complicated, and a complex manufacturingapparatus is required.

In order to solve the problems arising from using conventional CVD andALD methods, a new method is disclosed in U.S. Pat. No. 5,972,430 issuedto Dimeo in 1999. According to this method, the precursors containingthe respective constituent metal elements of a target layer aresimultaneously supplied into a reactor to form a precursor layer, andthe reactor is purged with an inert gas. Next, all the metal atoms ofthe precursor layer are oxidized by an oxidizing agent, therebyresulting in a multicomponent metal oxide layer. Then, the reactor ispurged again with an inert gas. This process cycle is repeated in orderto complete the film formation. However, simultaneous supply of theprecursors containing the respective constituent metal atoms in thismethod causes reaction between the constituent metal atoms, therebylowering the vapor pressure. Precursors having low vapor pressure, suchas Ba(thd)₂ or TaCl₅, are easily changed from a gas phase to a solidphase as the temperature-drops. This phase transition occurs easily whenvaporized precursors are in transit states of being supplied into an ALDreactor. In addition, during the phase transition from vapor to solid,particles are easily generated during each transition going from a vaporstate to a solid state. Once particles are generated, removing as wellas handling of such particles is very difficult. Ba(thd)₂ and Sr(thd)₂,which are Ba and Sr precursors, respectively, react with an alkyl groupprecursor to form a compound having a low vapor pressure, which isdifficult to handle. Here, the abbreviation “thd” stands fortetramethylheptanedionate ((CH)₃CC(O)CHC(O)C(CH)₃).

ALD methods, in which source gases containing the respective atomsconstituting a target layer are separately supplied, can preventreaction between the constituent atoms. However, when an organometalliccompound is used as a precursor, the temperature of a substrate shouldbe kept lower than the temperature of the organometallic compoundbecause an organometallic compound is easily decomposed by itself at ahigh temperature, and easily form a solid state. Furthermore, if thetemperature of the substrate is too low, the target layer cannot beformed because a desired reaction does not occur between supplied sourcegases. Thus, there is a need to maintain the substrate at a temperaturegreater than a minimal temperature at which formation of the targetlayer is caused. The range of minimum and maximum reaction temperaturesof a substrate for ALD methods is varied depending on source materials.To form a multi-atomic layer by ALD, source materials containing therespective constituent atoms of the multi-atomic layer should have anoverlapping range of minimum and maximum reaction temperatures. If atarget layer is composed of many kinds of atoms so that there is nooverlapping range of reaction temperatures between the constituentatoms, ALD methods cannot be applied to form the target layer. Inaddition, it is impossible to deposit a pure metal layer such as a Ti,W, or Al layer at a temperature lower than the thermal decompositiontemperature of the metal layer by conventional ALD methods.

To form a layer with source materials having low reactivity, U.S. Pat.No. 5,916,365 to Sherman et al. discloses a thin film formations methodinvolving supplying a first reactant gas into a reactor, exhausting theremaining first reactant gas from the reactor with a vacuum pump,supplying a second reactant gas which is activated passing through aradical generator such as a radio frequency (RF) power supply unit, andexhausting the remaining second reactant gas from the reactor with thevacuum pump. However, the pumping rate of the vacuum pump decreases asthe pressure in the reactor decreases. Thus, it takes a considerableamount of time to fully exhaust the remaining reactant gas from thereactor.

To solve such problem, Korean Patent Application No. 99-11877 disclosesa method of forming a thin film by generating plasma in synchronizationwith cyclic operation processes, which is incorporated herein byreference. The cyclic operation processes involve supplying a reactantgas, exhausting the remaining reactant gas from the reactor with a purgegas, supplying another reactant gas, and purging the reactor with apurge gas. Exhausting the remaining reactant gas using a purge gas isfaster than using a vacuum pump. Thus, the method of Korean PatentApplication No. 99-11877 can shorten the gas supply time with animproved film growth rate, compared to the method disclosed in U.S. Pat.No. 5,916,365. When plasma is directly generated in a reactor for afaster reaction rate, the method by Sherman et al. causes a seriouschange in gas pressure of the reactor, thereby destabilizing plasma.However, use of a purge gas can maintain the pressure of the reactorconstant, thereby enabling stable plasma generation. In addition, tosupply a solid material such as a barium (Ba) source used in theformation of a barium titanate layer at a constant rate, a liquid sourcesupply unit for supplying a solution in which a solid material isdissolved in a solvent, and a vaporizer for converting a liquid sourcematerial to a gaseous form, are used. In this case, the method bySherman et al. leads to clogging of the liquid source supply unit. Inparticular, when the reaction chamber is evacuated with a vacuum pump topurge a gaseous material that remains after reaction induced bysupplying a reaction source, a highly volatile solvent rapidlyevaporates near the supply line of the liquid source connected to thevaporizer. As a result, a viscous solid material remains in the liquidsource supply unit and clogs the supply line of the liquid source. Incontrast, the method disclosed in Korean Patent Application No. 99-11877does not cause such a problem because the pressure of the reactor andthe vaporizer is maintained at a constant level.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of forforming a metal layer, a metal oxide layer, or a metal nitride layer ona semiconductor or flat-panel display substrate with superiorcharacteristics by chemical vapor deposition (CVD) in which atime-divisional sequentially-pulsed source supply technique is usedalong with plasma in synchronization with the sequentially pulsed sourcesupply cycle.

In the present invention, a radio-frequency (RF) power of 0.01-2.0 W/cm²is applied as pulses for plasma generation in synchronization with thecycle of pulsing reactant gases. Here, RF power means a maximum powerlevel upon the application of power pulse. The plasma generation may becontinuous rather than pulsed. When an atomic layer deposition (ALD)method using plasma is applied, the minimum reaction temperature atwhich source materials can be deposited into a layer is lowered. As aresult, the range of reaction temperature at which a layer can be formedby ALD, from the maximum temperature to the minimum temperature, becomesbroader. Therefore, although the ALD method is applied with many kindsof atoms to form a multi-atomic layer, an overlapping reactiontemperature range between the atoms exists, thereby enabling formationof the multi-atomic layer by ALD. In other words, ALD using plasma(hereinafter, “plasma ALD”) is less limited in the range of minimum andmaximum reaction temperatures, and thus selection of metallic sourcematerials is also less limited, compared to a general ALD method notusing plasma. In addition, when a pure metal layer is deposited usingAl, Ti, or W, plasma serves as an activation energy source so that anatomic layer can be deposited at a temperature lower than the thermaldecomposition temperature of the source material. The physical andchemical properties of the resultant layer can be varied and improved bychanging the level of RF power pulses applied to generate plasma.

According to the present invention, the step of generating plasma can becarried out after each cycle of pulsing reactant gases, or after severalcycles of pulsing reactant gases. For example, a TiN layer with improvedcharacteristics can be formed by pulsing reactant gases and generatingplasma in the following sequence:[(Ti→N)→(N or H plasma)]or[{(Ti→N)}_(n cycles)→(N or H plasma)].

Here, to prevent unnecessary pre-reaction between source materials, thereactor is purged with a purge gas before and after each supply ofsource materials.

According to the present invention, by using the source materials thatdo not react with each other when the plasma is absent, the pulsing stepof the reactor with a purge gas between each supply of source materialscan be omitted. For example, oxygen gas (O₂) slowly reacts with ametallic compound at low temperatures, whereas oxygen plasma easilyreacts with a metallic compound to form a metal oxide. In this case, ametal oxide layer can be formed without using a purge gas by pulsingmaterials in the following sequence:[(metallic source)→oxygen gas→(oxygen plasma)→].

As a result, the deposition rate of the metal oxide layer is improved,compared to the method using a purge gas. As another example, a metalnitride layer can be formed using nitrogen gas (N₂) and hydrogen gas(H₂) which do not react with a metallic source, by pulsing materials inthe following sequence:[(metallic source)→(nitrogen gas+hydrogen gas)→(nitrogen and hydrogenplasma)→].

In this case, the metal oxide layer is deposited at a higher rate,compared to the method using a purge gas. A metal nitride layer can beformed by generating ammonia (NH₃) plasma in a reactor, instead of usingnitrogen gas (N₂) and hydrogen gas (H₂). However, the use of nitrogengas (N₂) and hydrogen gas (H₂) is advantageous in that a purge gas isnot used during the processing cycle for the metal nitride layer.According to the present invention, a pure metal layer of Ti, Al, or Wcan be formed at low temperatures by repeating the following cycle:[(metallic source)→hydrogen gas→(hydrogen plasma)→].

According to the present invention, oxygen gas, hydrogen gas, and amixture of nitrogen and hydrogen can be mixed with an inert gas such ashelium (He) or argon (Ar) to be used as a purge gas for improved purgingeffects. The addition of an inert gas also allows reactivity to becontrolled by varying the concentration of reactant gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail preferred embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a flowchart illustrating an atomic layer deposition (ALD)method for forming a metal oxide layer according to a first preferredembodiment of the present invention;

FIG. 2 is a flowchart illustrating a conventional method for forming ametal oxide layer, as a comparative example to the first embodiment ofthe ALD method according to the present invention;

FIG. 3 is a flowchart illustrating an ALD method for forming a tantalumoxide (Ta₂O₅) layer according to a second embodiment of the presentinvention; and

FIG. 4 is a flowchart illustrating a conventional method for forming atantalum oxide (Ta₂O₅) layer, as a comparative example to the secondembodiment of the ALD method according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention now will be described more fully and in detailwith reference to the accompanying drawings by providing preferredembodiments as described below.

Embodiment 1

Oxygen gas (O₂) reacts slowly with an organometallic source material sothat it is difficult to form a metal oxide layer at a temperature of400° C. or less with oxygen gas and an organometallic source material.Although a metal oxide layer can be formed with oxygen gas and anorganometallic source material, the film formation rate is very slow.Thus, in the present embodiment, a method of forming an aluminum oxidelayer using oxygen plasma is described. FIG. 1 is a flowchartillustrating an ALD method according to a first embodiment of thepresent invention.

As shown in FIG. 1, an aluminum oxide (Al₂O₃) layer was formed usingtrimethylaluminum (TMA) as an aluminum source at a substrate temperatureof 200° C. at a reactor pressure of 3 torr. To form the aluminum oxidelayer, TMA is supplied for 0.2 seconds, argon (Ar) for 0.4 seconds, andoxygen gas (O₂) for 0.4 seconds in sequence, and directly followed byoxygen plasma generation for 1 second (Step 103 through 106 of FIG. 1).The sequential pulses of gases and plasma generation for 2 seconds intotal are referred to as a cycle. Here, a radio frequency (RF) power of150 W is applied for 1 second to generate oxygen plasma. The completionof one cycle results in an aluminum oxide layer having a thickness of1.6 Å.

A conventional ALD method, which is reported in an article entitled“Perfectly Conformal TiN and Al₂O₃ films Deposited by Atomic LayerDeposition”, Chemical Vapor Deposition, Vol. 5, No. 2, p. 7, 1999 byRitala et al., is shown in FIG. 2. The conventional method of FIG. 2 forforming an aluminum oxide layer involves, without generation of plasma,supplying TMA (1.5 sec)→N₂ (0.5 sec)→H₂O (3.0 sec)→N₂ (0.5 sec), whichforms a cycle of 5.5 seconds (Steps 202 through 205 of FIG. 1). Here,the completion of one cycle results in an aluminum oxide layer having athickness of 1.1 Å.

Compared with the conventional method of FIG. 2, the ALD methodaccording to the present invention can form a 46% thicker aluminum oxidelayer (1/6 Å/1.1 Å=1.46) per operation cycle. The film formation rate ofthe ALD method according to the present invention calculated based uponthe thickness difference is four times greater compared to theconventional method. Therefore, the ALD method according to the presentinvention using oxygen gas having low reactivity and oxygen plasma canform an aluminum oxide layer four times faster, compared to theconventional ALD method using highly reactive gases.

Embodiment 2

FIG. 3 is a flowchart illustrating a second embodiment of an ALD methodfor forming a tantalum oxide (Ta₂O₅) layer according to the presentinvention. As shown in FIG. 3, a tantalum oxide (Ta₂O₅) layer was formedusing dimethoxyamidoethyltetraethyltantalum(Ta(OC₂H₅)₄(OCH₂(CH₂N(CH₃)₂), TAE(dmae)) as a tantalum source at asubstrate temperature of 250° C. at a reactor pressure of 4 torr. Toform the tantalum oxide layer, the sequential processing step ofTAE(dmae) (0.3 sec)→Ar(1.7 sec)→O₂ (1 sec)→(O₂+plasma) (2 sec)→Ar(1 sec)is followed, during which cycle a plasma is generated for 2 seconds withoxygen (O₂) gas. The sequential pulses of gases and plasma generationtotaling 6 seconds are referred to as a cycle (Step 303 through 307 ofFIG. 3). Here, a radio frequency (RF) power of 180 W is applied for 2seconds in order to generate oxygen plasma. The completion of one cycleresulted in a tantalum oxide layer having a thickness of 0.67 Å.

A conventional ALD method, which is reported in an article entitled“Atomic Layer Epitaxy Growth of Tantalum Oxide Thin Films from(Ta(OC₂H₅)₅ and H₂O”, Journal of Electrochemical Society, Vol. 142, No.5, p. 1670, 1995 by K. Kukli et al. is shown in FIG. 4. The conventionalmethod of FIG. 4 for forming an tantalum oxide layer involves, withoutplasma treatment by using the sequential processing step ofTa(OC₂H₅)₅(0.2 sec)→N₂ (time duration not specified)→H₂O (2.0 sec)→N₂(time duration not specified), which forms a cycle (Steps 402 through405 of FIG. 4) time of 2.4 seconds or longer. Here, the completion ofone cycle resulted in a tantalum oxide layer having a thickness of 0.4Å.

Since the purging duration of nitrogen into the reactor is not describedin the article, the film formation rate per operation cycle cannot becompared accurately with the ALD method according to the presentinvention. However, from a simple comparison in film thickness betweenthe present invention and the conventional method, it is apparent thatthe ALD method according to the present invention can form a tantalumoxide layer 68% (0.67/0.4=68%) faster, compared to the conventional ALDmethod. Therefore, the ALD method according to the present inventionusing oxygen gas having low reactivity and oxygen plasma can form atantalum oxide layer 68% faster based upon the thickness of theresulting tantalum oxide layers, compared to the conventional ALD methodusing highly reactive gases.

Embodiment 3

The present embodiment is directed to a plasma ALD method for forming astrontium titanate (SrTiO₃; STO) layer. STO or barium strontium titanate((Ba,Sr)TiO₃; BST) has greater dielectric constant so that they are usedas a dielectric material for capacitors of highly integrated memorydevices such as DRAMs.

A source material Sr(thd)₂, where abbreviation “thd” stands fortetramethylheptanedionate, is supplied into a reactor and then thereactor is purged with argon (Ar). Next, oxygen gas is supplied into thereactor to generate plasma and then the reactor is purged again with Ar.Ti(O-i-Pr)₄ [or Ti(O-i-Pr)₂(thd)₂] is supplied into the reactor, and thereactor is purged again with Ar gas. Next, oxygen gas is supplied intothe reactor to generate plasma and then the reactor is purged with Ar.This cycle is repeated one or more times until a STO layer having adesired thickness is obtained.

Embodiment 4

The present embodiment is directed to a plasma ALD method for forming aBST layer. A source material Ba(thd)₂ is supplied into a reactor andthen the reactor is purged with argon (Ar). Next, oxygen gas is suppliedinto the reactor to generate plasma and then the reactor is purged againwith Ar. This cycle is repeated with Ti(O-i-Pr)₄ [or Ti(O-i-Pr)₂(thd)₂]and then Sr(thd)₂. Next, Ti(O-i-Pr)₄ (or Ti(O-i-Pr)₂(thd)₂) is suppliedagain into the reactor and followed by purging with Ar, supply of oxygento generate oxygen plasma, and then purging with Ar. The cycle ofsupplying source materials in the sequence of Ba→O→Ti→O→Sr→O→Ti→O isrepeated one or more times until a BST layer is formed to a desiredthickness. Alternately, the sequence of supplying source materials canbe changed to a sequence of Ba→O→Sr→O→Ti→O→Ti→O, or a sequence ofSr→O→Ba→O→Ti→O→Ti→O and then repeated until a BST layer having a desiredthickness is formed.

The composition ratio of Ba: Sr:Ti can be varied by repeating anadditional cycle of supplying a desired material. For example, for ahigher ratio of Ba to Sr, the cycle of supplying source materials in thesequence of Ba→O→Ti→O→Sr→O→Ti→O is extended to further include asub-cycle of supplying Ba₆O₆Ti₆O, thereby forming a BST layer having adesired thickness.

In Embodiments 3 and 4, Ba(thd)₂[or Sr(thd)₂] may be dissolved in asolvent such as tetrahydrofuran (THF) or n-butylacetate and thensupplied into the reactor through a liquid source supply unit and avaporizer. In this case, the amounts of source materials supplied duringeach cycle can be controlled with improved consistency.

Embodiment 5A

A ferroelectric layer such as strontium bismuth tantalate (SrBi₂Ta₂O₉;SBT) or lead zirconate titanate (Pb(Zr,Ti)O₃; PZT) is used in themanufacture of nonvolatile memory devices capable of retaining data whenpower is turned off. Formation of a SBT layer will be described inEmbodiments 5A and 5B, and formation of a PZT layer will be described inEmbodiment 6.

A source material Sr(thd)₂ is supplied into a reactor and the reactor ispurged with Ar. Next, oxygen gas is supplied into the reactor togenerate plasma and the reactor is purged again with Ar. This cycle isrepeated with triphenylbismuth (BiPh₃) and Ta(OEt)₅, respectively. Here,Ta(OEt)₅ and Bi(Ph₃) can be replaced with Ta(OEt)₄(dmae) and Bi(thd)₃,respectively. The abbreviation “dmae” stands for dimethylaminoetoxide.

Following this, Bi(thd)₃ or triphenylbismuth (BiPh₃) is supplied intothe reactor, and the reactor is purged with Ar. Next, oxygen gas issupplied into the reactor to generate plasma, and the reactor is purgedwith Ar. Next, this cycle is repeated with Ta(OEt)₅ or Ta(OEt)₄(dmae).Here, Ta(OEt)₅ can be replaced with Ta(OEt)₄(dmae).

The cycle of supplying source materials in the sequence ofSr→O→Bi→O→Ta→O→Bi→O→Ta→O is repeated one or more times until a SBT layeris formed to a desired thickness. The composition ratio of Sr:Bi:Ta canbe varied by further repeating a sub-cycle of supplying a targetmaterial during one or more cycles of the source material supply.

Embodiment 5B

In the present embodiment, an ALD method for forming a SBT layer usingSr[Ta(OEt)₆]₂ (where Sr:Ta=1:2) or Sr[Ta(OEt)₅(dmae)]₂ is disclosed.

Sr[Ta(OEt)₆]₂ or Sr[Ta(OEt)₅(dmae)]₂ is supplied into a reactor, and thereactor is purged with Ar gas. Next, oxygen gas is supplied into thereactor to generate plasma and followed by purging with Ar gas. Next,Bi(thd)₃ or BiPh₃ is supplied into the reactor, the reactor is purgedwith Ar gas, and oxygen gas is supplied into the reactor to generateplasma and followed by purging with Ar gas. The cycle of supplying abismuth source and oxygen is repeated twice. This cycle of supplyingsource materials in the sequence of SrTa₂→O→Bi→O→Bi→O is repeated one ormore times until a SBT layer is formed to a desired thickness. Thecomposition ratio of Sr:Bi:Ta can be varied by further repeating oromitting a sub-step of supplying a bismuth source material during one ormore cycles of the source material supply, thereby resulting in a SBTlayer having a desired thickness.

In Embodiments 5A and 5B, Bi(thd)₃, BiPh₃, Sr[Ta(OEt)₆]₂, andSr[Ta(OEt)₅(dmae)]₂ may be dissolved in a solvent such as THF orn-butylacetate and then supplied into the reactor through a liquidsource supply unit and a vaporizer. In this case, the amounts of sourcematerials supplied during each source material supply cycle can becontrolled with improved consistency.

Embodiment 6

A plasma ALD method for forming a PZT layer is disclosed in the presentembodiment. Pb(thd)₂ is supplied into a reactor, and the reactor ispurged with Ar. Next, oxygen gas is supplied into the reactor togenerate plasma and followed by purging with Ar. Next, this cycle isrepeated with Zr(O-t-Bu)₄ [or Zr(O-t-Bu)₂(thd)₂] and Pb(thd)₂. Finally,Ti(O-i-Pr)₄ [Ti(O-i-Pr)₂(thd)₂] is supplied into the reactor andfollowed by purging with Ar, supply of oxygen to generate plasma, andpurging with Ar. This cycle of supplying source materials in thesequence of Pb→O→Zr→O→Pb→O→Ti→O is repeated one or more times until aPZT layer is formed to a desired thickness. The composition ratio ofPb:Zr:Ti can be varied by further repeating or omitting a sub-cycle ofsupplying a particular material source during the source material supplycycle. For example, in the sequential process cycle Pb→O→Zr→O→Pb→O→Ti→O,the sub-cycle Ti→O may be added or subtracted and/or the sub-cycle Zr→Omay be added in order to change the ratio of Zr:Ti.

Solid materials such as Pb(thd)₂, Zr(O-t-Bu)₂(thd)₂, andTi(O-i-Pr)₂(thd)₂ may be dissolved in a solvent such as THF orn-butylacetate and then supplied into the reactor through a liquidsource supply unit and a vaporizer. In this case, the amounts of sourcematerials supplied during each source material supply cycle can becontrolled with improved consistency.

Embodiment 7A

A zirconium silicate (Zr—Si—O) and hafnium silicate (Hf—Si—O), whichhave much higher dielectric constant than silicon dioxide (SiO₂), areknown to be suitable materials for a gate insulating layer fortransistors.

In the present embodiment, a plasma ALD method for forming a Zr—Si—Olayer is described. t-butoxyzirconium [Zr(O-t-Bu)₄] is supplied into areactor, and the reactor is purged with Ar. Next, oxygen gas is suppliedinto the reactor to generate plasma and followed by purging with Ar.Next, tetraethoxysilicon (TEOS) is supplied into the reactor andfollowed by purging with Ar, supply of oxygen gas to generate plasma,and purging with Ar. This cycle of supplying source materials isrepeated one or more times until a Zr—Si—O layer is formed to a desiredthickness.

Embodiment 7B

A plasma ALD method for forming a Hf—Si—O layer according to the presentinvention is disclosed. t-butoxyhafnium [Hf(O-t-Bu)₄] is supplied into areactor, and the reactor is purged with Ar. Next, oxygen gas is suppliedinto the reactor to generate plasma and followed by purging with Ar.Next, TEOS is supplied into the reactor and followed by purging with Ar,supply of oxygen gas to generate plasma, and purging with Ar. This cycleof supplying source materials is repeated one or more times until aHf—Si—O layer is formed to a desired thickness.

Embodiment 8

In the present embodiment, an ALD method for forming an aluminum layer,which is used for metal interconnections in the manufacture ofsemiconductor devices, using a trialkylaluminum (Al(C_(n)H_(2n+1))₃,n=1-6) source material and hydrogen (H₂) plasma is disclosed. Suitabletrialkylaluminum group materials include trimethylaluminum [Al(CH₃)₃],triethylaluminum [Al(C₂H₅)₃], and triisobutylaluminum[Al(CH₂CH(CH₃)₂)₃]. The higher the temperature at which the aluminumlayer is formed, the greater the conductivity of the aluminum layer.Therefore, trimethylammonium having a highest thermal decompositiontemperature is preferred for a higher reaction temperature for ALD.

First, trialkylaluminum (Al(C_(n)H_(2n+1))₃, n=1-6) is supplied into areactor, and the reactor is purged with Ar. Next, hydrogen (H₂) gas issupplied to generate plasma. Here, plasma can be generated after orwhile hydrogen gas is supplied. Then, the reactor is purged again withAr. That is, the sequence of the cycle of supplying source materials isillustrated as:R₃Al→Ar→(H₂)→(H₂+plasma)→Ar.

Here, hydrogen gas does not react with trialkyaluminum(Al(C_(n)H_(2n+1))₃, n=1-6) and thus subsequent purging with Ar can beomitted, thereby reducing time required for each source material supplycycle with improved film formation rate. In this case, after supplyingtrialkylaluminum (Al(C_(n)H_(2n+1))₃, n=1-6) into a reactor, hydrogengas is supplied into the reactor, and plasma is generated apredetermined time later. Next, the generation is of plasma is stopped,and the supply of the hydrogen gas is cut off immediately or about 1second later. This cycle of supplying materials and generating plasma isrepeated to form an aluminum layer. This operation cycle is illustratedas:R₃Al→H₂→(H₂+plasma)orR₃Al→H₂→(H₂+plasma)→H₂  (#1 second)

Embodiment 9A

Aluminum is commonly used for connection of a transistor, capacitor, orresistor in a semiconductor substrate or for power supply to the same.Recently, copper is also used for the same purpose. In this case, when aplasma ALD method is applied to form a copper diffusion barrier layer,such as a TaN layer or a Ta—N—C layer, the electrical conductivity ofthe copper diffusion barrier layer is increased, compared to other ALDmethods not using plasma. For example, compared to an ALD methodinvolving repeatedly supplying an amido compound or amido-imido compoundof Ta and ammonia gas (NH₃), the ALD method according to the presentinvention further involving a plasma generation step can produce adiffusion barrier layer for copper with greater electrical conductivity.Alternatively, the electrical conductivity of the diffusion barrierlayer for copper can be improved by an ALD method that involves a stepof supplying activated nitrogen plasma, instead of the step of supplyingammonia gas.

A Ta—N layer [or a Ta—N—C layer] can be formed by plasma ALD methodusing t-butylimido-tris(diethylamido)tantalum (TBTDET) as a Ta source.An ALD method carried out by repeatedly supplying source materials inthe sequence of TBTDET→Ar→NH₃→Ar results in a Ta—N layer [or Ta—N—Clayer] having a greater resistivity on the order of 10⁸ μΩ·cm. Incontrast, the plasma ALD method with the operation cycle ofTBTDET→Ar→NH₃→Ar→(H₂+plasma) results in a Ta—N layer [or Ta—N—C layer]is having a much lower resistivity of 4400 μΩ·cm-. In addition, a Ta—N—Clayer (containing 15-40% carbon) formed by a plasma ALD method with theoperation cycle of TBTDET→H₂→(H₂+plasma) has a much lower resistivity of400 μΩ·cm.

Embodiment 9B

A plasma ALD method for forming a titanium nitride layer usingtetrakis(dimethylamido)titanium (TDMAT) as a titanium source isdisclosed. A TiN layer formed by an ALD method with the operation cycleof TDMAT→Ar→NH₃Ar has a resistivity of 1000 μΩ·cm. In contrast, a TiNlayer formed by a plasma ALD method with tens to hundreds of repetitionsof the cycle of TDMAT→Ar→NH₃→Ar→(H₂+plasma) has a much lower resistivityof 1800 μΩ·cm.

Embodiment 10

A plasma ALD method for forming a titanium nitride (TiN) layer or atantalum nitride (TaN) layer using nitrogen (N₂) gas, which is almostnot reactive, is disclosed. A TiN layer or a TaN layer is depositedusing TiCl₄ as a titanium source or TaCl₅ as a tantalum source at asubstrate temperature of 300° C. at a reactor pressure of 5 torr. Here,the cycle of supplying TiCl₄ [or TaCl₅] (0.2 sec)→(N₂+H₂) (1.2sec)→(plasma generation (2.0 sec) is repeated to form the TiN layer orthe TaN layer. To supply the gas mixture of N₂ and H₂ as a reactant gasand purge gas, each of N₂ and H₂ is supplied at a flow rate of 60 sccm.The plasma is generated with the application of a radio-frequency (RF)power of 150 W (for an 8-inch wafer). The TiN layer [or TaN layer]formed during one operation cycle has a thickness of 0.5 Å. Here, thecomposition of the TiN layer [or the TaN layer] can be varied bycontrolling the flow rate of N₂ [or H₂] For example, only N₂ can besupplied. Alternatively, the content of Ti [or Ta] in the TiN layer [orthe TaN layer] can be adjusted by the ratio of H₂ in the gas mixture. Ifthe temperature of the substrate is too low during reaction, TiCl₄ [orTaCl₅] particles are formed by condensation. If the temperature of thesubstrate is too high, it is undesirable for interconnect materials.Therefore, it is preferable to maintain the substrate temperature duringreaction within the range of 150-500° C. It is preferable that thereactor pressure is in the range of 0.5-10 torr with a RF power of0.01-2.0 W/cm² for plasma generation.

Embodiment 11

Metals such as aluminum (Al) are used for connection of a semiconductordevices, capacitors, and resistors on a silicon substrate or for powersupply to the same. Recently, copper is also used for the same purpose.In this case, a diffusion barrier layer, such as a TiN or TaN layer, forblocking diffusion of copper atom into an insulating layer is required.The TiN or TaN layer has poor adhesion to copper. Therefore, a methodfor depositing a diffusion barrier layer without this problem isdisclosed in the present embodiment.

A halogen gas such as Ti [or Ta], or an organometallic compound issupplied into a reactor, and the rector is purged with Ar. Ammonia ornitrogen gas is supplied into the reactor and followed by generation ofplasma and purging with Ar. This cycle is repeated until a TiN [or TaN]layer is formed to be thick enough to prevent diffusion of copper atominto the insulating layer. Following this, (hfac)Cu⁺¹ (vtms) [orCu(hfac)₂] is supplied into the reactor and followed by purging with Ar.Hydrogen gas is supplied into the reactor to discharge plasma andfollowed by purging with Ar, thereby forming a copper layer on thesurface of the substrate. As a result, an Al layer with good adhesion toa copper layer can be formed by this method.

Embodiment 12

A plasma ALD method for forming a copper diffusion barrier layer withimproved adhesion to a copper layer is disclosed. First, a TiN layer [ora TaN layer] is formed to be thick enough for blocking diffusion ofcopper atoms by repeating the operation cycle for the TiN layer [or TaNlayer]. Here, the processing sub-cycle for forming a metallic layer withgood adhesion is repeated during the processing cycle of forming the TiNlayer or [TaN layer]. For example, a sub-cycle including two runs of thesupply cycle of Ti [or Ta]→Ar→N→Ar and a single run of the supply cycleof Cu [or Al]→Ar→H→Ar is repeated twice. Next, another sub-cycleincluding a single run of the supply cycle of Ti [or Ta]→Ar →N→Ar and asingle run of the supply cycle of Cu [or Al]→Ar→H→Ar is repeated twice.Then, another sub-cycle including a single run of the supply cycle of Ti[or Ta]→Ar →N→Ar and two runs of the supply cycle of Cu [or Al]→Ar→H→Aris repeated twice. Finally, the supply cycle of Cu [or Al]→Ar→H→Ar isrepeated three times. By forming the TiN [or TaN] layer as a diffusionbarrier layer with a gradually varying composition profile, improvedadhesion between the diffusion barrier layer and a copper interconnectlayer has been obtained as a result.

Embodiment 13

A plasma ALD method for forming a titanium (Ti) layer or a tantalum (Ta)layer, in which plasma is generated in synchronization with the cycle ofpulsing source materials, is disclosed. Here, a Ti layer [or a Ta layer]is formed using TiCl₄ as a titanium source [or TaCl₅] as a tantalumsource at a substrate temperature of 300° C. and at a reactor pressureof 5 torr. Here, the processing cycle of supplying TiCl₄ [TaCl₅] (0.2sec)→H₂ (1.9 sec)→(plasma generation) (2.0 sec) is repeated to form theTiN layer [or the TaN layer]. The plasma is generated with theapplication of a radio-frequency (RF) power of 150 W (for an 8-inchwafer). Although H₂ is used as a reactant gas and purge gas in thepresent embodiment, a mixture with an inert gas such as helium (He) orAr can be used for purging efficiency. If the temperature of thesubstrate is too low during reaction, TiCl₄ or TaCl₅ particles areformed by condensation. If the temperature of the substrate is too high,it is undesirable for interconnect materials. Therefore, it ispreferable to maintain the substrate temperature during reaction withinthe range of 150-500° C. It is preferable that the reactor pressure isin the range of 0.5-10 Torr with a RF power of 0.01-2.0 W/cm² for plasmageneration.

Embodiment 14

A plasma ALD method for forming a tungsten (W) layer, in which plasma isgenerated in synchronization with the cycle of pulsing source materials,is disclosed. Here, a W layer is formed using WF₆ as a tungsten sourceat a substrate temperature of 300° C. and at a reactor pressure of 5torr. Here, the processing cycle of WF₆ (1.0 sec)→(H₂+Ar) (6.0sec)→(plasma generation) (2.0 sec) is repeated to form the W layer.Here, WF₆ is supplied at a flow rate of 2 sccm, and N₂ and Ar gases usedas a reactant gas and a purge gas, respectively, are supplied at a flowrate of 100 sccm, respectively. The plasma is generated at aradio-frequency (RF) power of 100 W (for an 8-inch wafer). It ispreferable to maintain the substrate temperature during reaction withinthe range of 100-450° C. It is preferable that the reactor pressure isin the range of 0.5-10 torr with a RF power of 0.01-2.0 W/cm² for plasmageneration.

Embodiment 15

A plasma ALD method for forming a tungsten nitride (WN) layer, in whichplasma is generated in synchronization with the cycle of pulsing sourcematerials, is disclosed. Here, a WN layer is formed using WF₆ as atungsten source at a substrate temperature of 300° C. and at a reactorpressure of 5 torr. Here, the processing cycle of WF₆ (1.0 sec)→(H₂+N₂)(6.0 sec)→(plasma generation) (2.0 sec) 6 (H₂+N₂) (1 sec) is repeated toform the WN layer. Here, WF₆ is supplied at a flow rate of 2 sccm, andN₂ and H₂ gases used as a reactant gas and a purge gas are supplied at aflow is rate of 100 sccm and 50 sccm, respectively. The plasma isgenerated at the radio-frequency (RF) power of 100 W (for an 8-inchwafer). Here, the composition of the WN layer can be varied by adjustingthe flow rate of N₂ [or H₂]. Only N₂ can be supplied without H₂. Thecontent of W in the WN layer can be varied by adjusting the ratio of H₂in the gas mixture. It is preferable to maintain the substratetemperature during reaction within the range of 100-450° C. It ispreferable that the reactor pressure is in the range of 0.5-10 torr witha RF power of 0.01-2.0 W/cm² for plasma generation.

While this invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A method for forming a metal-containing layer on a substrate in a reactor of an atomic layer deposition (ALD) apparatus, the method comprising a plurality of ALD cycles of sequential reactant pulses, the cycles comprising: pulsing a first metallic source compound into the reactor; supplying a reactant gas into the reactor without generating a plasma, where the reactant gas does not react with the first metallic source compound in the absence of plasma; and generating a plasma directly in the reactor while continuing to supply the reactant gas into the reactor; and repeating pulsing the first metallic source compound, supplying the reactant gas and generating the plasma directly in the reactor until the metal-containing layer is formed to a desired thickness.
 2. The method of claim 1, wherein the metallic source compound comprises an organometallic compound.
 3. The method of claim 1, wherein generating the plasma is conducted in each of the cycles.
 4. The method of claim 1, wherein generating the plasma is conducted after several cycles of supplying the metallic source compound.
 5. The method of claim 1, wherein the reactant gas comprises O₂ and the metal-containing layer comprises a metal oxide layer.
 6. The method of claim 5, wherein the first metallic source compound is trimethylaluminum (Al(CH₃)₃), and the metal oxide layer is an aluminum oxide (Al₂O₃) layer.
 7. The method of claim 5, wherein the first metallic source compound is dimethoxyamidoethoxytetraethoxytantalum (Ta(OC₂H₅)₄(OC₂H₄N(CH₃)₂) or ethoxytantalum (Ta(OC₂H₅)₅), and the metal-containing layer is a tantalum oxide (Ta₂O₅) layer.
 8. The method of claim 5, wherein one or more of the ALD cycles further comprises pulsing a second metallic source compound into the reactor, wherein the metal-containing layer comprises a complex metal oxide layer.
 9. The method of claim 8, further comprising: supplying the O₂ reactant gas into the reactor without generating a plasma after pulsing the second metallic source compound; generating a plasma directly in the reactor while continuing to supply the O₂ reactant gas; and repeating pulsing the first metallic source compound, supplying the O₂ reactant gas, generating the plasma, pulsing the second metallic source compound, supplying the O₂ reactant gas and generating the plasma until the metal-containing layer is formed to the desired thickness.
 10. The method of claim 8, wherein the first metallic source compound comprises strontium, the second metallic source compound comprises titanium, and the complex metal oxide layer comprises strontium titanate (STO).
 11. The method of claim 8, wherein one or more of the ALD cycles further comprises pulsing a third metallic source compound into the reactor, wherein the complex metal oxide layer comprises at least three kinds of metals.
 12. The method of claim 11, wherein one of the metallic source compounds comprises barium, another of the metallic source compounds comprises titanium, another of the metallic source compounds comprises strontium, and the complex metal oxide layer comprises barium strontium titanate (BST).
 13. The method of claim 11, wherein one of the metallic source compounds comprises strontium, another of the metallic source compounds comprises bismuth, another of the metallic source compounds comprises tantalum, and the complex metal oxide layer comprises strontium bismuth tantalate (SBT).
 14. The method of claim 13, wherein a ratio of strontium-containing metallic source compound pulses to tantalum-containing metallic source compound is about 1:2.
 15. The method of claim 11, wherein one of the metallic source compounds comprises lead, another of the metallic source compounds comprises zirconium, another of the metallic source compounds comprises titanium, and the complex metal oxide layer comprises lead zirconium titanate (PZT).
 16. The method of claim 8, wherein the first metallic source compound comprises bismuth, the second metallic source compound comprises strontium and tantalum in a ratio of 1:2, and the complex metal oxide layer comprises strontium bismuth tantalate (SBT).
 17. The method of claim 5, wherein one of more of the ALD cycles further comprises pulsing a silicon-based compound into the reactor.
 18. The method of claim 17, wherein the first metallic source compound comprises zirconium and the metal oxide layer comprises zirconium silicate (Zr—Si—O).
 19. The method of claim 17, wherein the first metallic source compound comprises hafnium and the metal oxide layer comprises hafnium silicate (Hf—Si—O).
 20. The method of claim 1, wherein the reactant gas comprises hydrogen and the metal-containing layer comprises a metal layer.
 21. The method of claim 20, wherein the reactant gas further comprises an inert gas.
 22. The method of claim 20, wherein first metallic source compound comprises a trialkylaluminum (Al(C_(n)H_(2n+1))₃, n=1-6) and the metal layer comprises an aluminum layer.
 23. The method of claim 20, wherein the first metallic source compound comprises titanium tetrachloride (TiCl₄) and the metal layer comprises a titanium layer.
 24. The method of claim 23, wherein, during formation of the titanium layer, the temperature of a substrate in the reactor is maintained at 150-500° C., the inside of the reactor is maintained at a pressure of 0.5-10 torr, and an RE power of 0.01-2.0 W/cm² is applied to generate the plasma.
 25. The method of claim 20, wherein the first metallic source compound comprises tungsten hexafluoride (WF₆) and the metal layer comprises a tungsten layer.
 26. The method of claim 25, wherein, during deposition of the tungsten layer, the temperature of a substrate in the reactor is maintained at 100-450° C., the inside of the reactor is maintained at a pressure of 0.5-10 torr, and an RF power of 0.01-2.0 W/cm² is applied to generate the plasma.
 27. The method of claim 20, wherein the first metallic source compound comprises tantalum pentachloride (TaCl₅) and the metal layer comprises a tantalum layer.
 28. The method of claim 27, wherein, during deposition of the tantalum layer, the temperature of a substrate in the reactor is maintained at 150-500° C., the inside of the reactor is maintained at a pressure of 0.5-10 torn and an RE power of 0.01-2.0 W/cm² is applied to generate the plasma.
 29. The method of claim 1, wherein the reactant gas comprises nitrogen and the metal-containing layer comprises a metal nitride layer.
 30. The method of claim 1, wherein the reactant gas comprises a gas mixture of nitrogen and hydrogen and the metal-containing layer comprises a metal nitride.
 31. The method of claim 30, wherein the first metallic source material is titanium tetrachloride (TiCl₄), and the metal nitride layer is a titanium nitride (TiN) layer.
 32. The method of claim 31, wherein, during deposition of the titanium nitride layer, the temperature of the substrate in the reactor is maintained at 150-500° C., the inside of the reactor is maintained at a pressure of 0.5-10 Torr, and an RF power of 0.01-2.0 W/cm² is applied to generate the plasma.
 33. The method of claim 30, wherein the first metallic source compound is tantalum pentachloride (TaCl₅), and the metal nitride layer is a tantalum nitride (TaN) layer.
 34. The method of claim 1, wherein the reactant gas comprises hydrogen gas, further comprising pulsing ammonia gas between pulsing the first metallic source compound and generating the plasma, wherein the metal-containing layer comprises a highly conductive metal nitride layer.
 35. The method of claim 1, wherein the first metallic source compound comprises a tantalum based organometallic compound, the reactant gas comprises hydrogen and the metal-containing layer comprises tantalum nitride carbide layer.
 36. The method of claim 1, wherein supplying the reactant gas further comprises supplying an inert gas.
 37. The method of claim 1, further comprising supplying an inert gas into the reactor between pulsing the first reactant and supplying the reactant gas.
 38. The method of claim 1, further comprising varying ratios of pulses of the first, second and third metallic source components over time to form the metal-containing layer with a graded composition profile.
 39. The method of claim 1, wherein a rate of forming the metallic layer per ALD cycle is faster than an ALD method using a metallic source compound and a reactive gas in the absence of plasma, where the reactive gas is more reactive than the reactant gas. 